1. Field of the Invention
The invention relates to medical devices for transluminally accessing body lumens and cavities and, more particularly, to methods and devices for accessing the mammalian urinary tract.
2. Description of the Related Art
A wide variety of diagnostic or therapeutic procedures involves the introduction of a device through a natural access pathway such as a body lumen or cavity. A general objective of access systems, which have been developed for this purpose, is to minimize the cross-sectional area of the access lumen, while maximizing the available space for the diagnostic or therapeutic instrumentation. These procedures are especially suited for the urinary tract of the human or other mammal. The urinary tract is relatively short and substantially free from the tortuosity found in many endovascular applications.
Ureteroscopy is an example of one type of therapeutic interventional procedure that relies on a natural access pathway, which is the urethra, the bladder, which is a body cavity, and the ureter, another body lumen. Ureteroscopy is a minimally invasive procedure that can be used to provide access to the upper urinary tract, specifically the ureter and kidney. Ureteroscopy is utilized for procedures such as stone extraction, stricture treatment, or stent placement. Other types of therapeutic interventional procedures suitable for use with expandable sheath technology include endovascular procedures such as introduction of cardiac valve replacements or repair devices via a percutaneous access to the vasculature. Gastrointestinal procedures, again percutaneously performed, include dilation of the common bile duct and removal of gallstones.
To perform a procedure in the ureter, a cystoscope is placed into the bladder through the urethra. A guidewire is next placed, through the working channel of the cystoscope and under direct visual guidance, into the target ureter. Once guidewire control is established, the cystoscope is removed and the guidewire is left in place. A ureteral sheath or catheter is next advanced through the urethra over the guidewire, through the bladder and on into the ureter. The guidewire may now be removed to permit instrumentation of the ureteral sheath or catheter. A different version of the procedure involves leaving the guidewire in place and passing instrumentation alongside or over the guidewire. In yet another version of the procedure, a second guidewire or “safety wire” may be inserted into the body lumen or cavity and left in place during some or all of the procedure.
Certain current techniques involve advancing a flexible, 10 to 18 French, ureteral sheath or catheter with integral flexible, tapered obturator over the guidewire. Because axial pressure is required to advance and place each catheter, care must be taken to avoid kinking the sheath, catheter, or guidewire during advancement so as not to compromise the working lumen of the catheter through which instrumentation, such as ureteroscopes and stone extractors, can now be placed. The operator must also exercise care to avoid advancing the sheath or catheter against strictures or body lumen or cavity walls with such force that injury occurs to said body lumen or cavity walls.
One of the issues that arise during ureteroscopy is the presence of an obstruction or stenosis in the ureter, which is sometimes called a stricture, that prohibits a sheath or catheter with a sufficiently large working channel from being able to be advanced into the ureter. Such conditions may preclude the minimally invasive approach and require more invasive surgical procedures in order to complete the task. Urologists may be required to use sheaths or catheters with suboptimal central lumen size because they are the largest catheters that can be advanced to the proximal end of the ureter. Alternatively, urologists may start with a larger catheter and then need to downsize to a smaller catheter, a technique that results in a waste of time and expenditure. Finally, a urologist may need to dilate the ureter with a dilation system before placing the current devices, again a waste of time and a need for multiple devices to perform the procedure. In most cases, it is necessary for the urologist to perform fluoroscopic evaluation of the ureter to determine the presence or absence of strictures and what size catheter would work for a given patient.
Additional information regarding ureteroscopy can be found in Su, L, and Sosa, R. E., Ureteroscopy and Retrograde Ureteral Access, Campbell's Urology, 8th ed, vol. 4, pp. 3306-3319 (2002), Chapter 97. Philadelphia, Saunders, and Moran, M. E., editor, Advances in Ureteroscopy, Urologic Clinics of North America, vol. 31, No. 1 (February 2004).